TOKYO (AP) -- An adviser to Japanese Prime Minister Shinzo Abe ended a visit to North Korea on Friday but would not give details of his talks with leaders in Pyongyang.

Isao Iijima's three-day visit came amid a slight easing of tension on the Korean Peninsula after weeks of threats from the North aimed at Washington, Seoul and Tokyo.

Japan has not disclosed the purpose of Iijima's trip.

"I had serious and long hours of talks (with North Korean officials) during my visit," Iijima told reporters after he arrived in Beijing. He would not give details about the talks.

"I will not speak to any media," he said. "I plan to inform the prime minister about my talks."

Japan is a participant in now-dormant six-nation talks aimed at ending North Korea's nuclear weapons program, and its failure to inform its ally the U.S., or South Korea, about Iijima's visit beforehand raised eyebrows.

Glyn Davies, the top U.S. envoy on North Korea, who visited South Korea, China and Japan this week, said earlier he had hoped to learn more about Iijima's visit during his talks in Tokyo.

He made no comment to reporters Friday, however, as he finished talks at Japan's Foreign Ministry.

Japanese Foreign Minister Fumio Kishida on Friday said cooperation among Japan, the U.S. and South Korea is extremely important for resolving North Korean issues.

"We need to make effort in the future to ensure good communication among us," he told reporters when asked about complaints from South Korea over Iijima's visit.

Iijima also was a senior aide to former Japanese Prime Minister Junichiro Koizumi, who met with late North Korean leader Kim Jong Il in 2002 and 2004.

Tokyo officials hinted Iijima' visit was related to cases of Japanese kidnapped by the North decades ago.

However, Kishida refused to comment on the outcome of Iijima's visit. He reiterated Japan's official line that all outstanding bilateral issues including abductions, missile launches and nuclear development must be resolved comprehensively.